- The Mesozoic Era saw the breakup of the supercontinent Pangaea into the northern landmass of Laurasia and the southern landmass of Gondwanaland. Reptiles like dinosaurs became the dominant land animals during this period. Dinosaurs exhibited a wide range of sizes and many new species evolved over the Mesozoic Era. Evidence suggests some dinosaurs may have been warm-blooded and faster runners than previously believed.
2. Chapter: Geologic Time
Table of Contents
Section 3: Middle and Recent Earth
History
Section 1: Life and Geologic Time
Section 2: Early Earth History
3. • Trilobites are
small, hard-
shelled organisms
that crawled on
the seafloor.
Geologic Time
Life and Geologic Time
1
• They are considered
to be index fossils
because they lived over vast regions of
the world during specific periods of
geologic time.
4. • Paleontologists have been able to divide
Earth’s history into time units based on the
life-forms that lived only during certain
periods.
• This division of Earth’s history makes up the
geologic time scale.
The Geologic Time Scale
1
Life and Geologic Time
5. • Four major subdivisions of
geologic time are used—
eons, eras, periods, and
epochs.
• The longest subdivisions—
eons—are based upon the
abundance of certain
fossils.
1
Life and Geologic Time
Major Subdivisions of Geologic Time
6. • Next to eons, the longest
subdivisions are the eras,
which are marked by major,
striking, and worldwide
changes in the types of
fossils present.
1
Life and Geologic Time
Major Subdivisions of Geologic Time
7. • Periods are units of geologic time
characterized by the types of life existing
worldwide at the time.
• Periods can be divided into smaller units of
time called epochs.
• Eras are subdivided into periods.
1
Life and Geologic Time
Major Subdivisions of Geologic Time
• Epochs are also characterized by differences
in life-forms, but some of these differences
can vary from continent to continent.
8. • Sometimes it is possible
to distinguish layers of
rock that formed during
a single year or season.
• In other cases, thick
stacks of rock that have
no fossils provide little
information that could
help in subdividing
geologic time.
Dividing Geologic Time
1
Life and Geologic Time
9. • The fossil record shows that species have
changed over geologic time.
• This change through time is known as
organic evolution.
Organic Evolution
1
• Organisms that are not adapted to changes
are less likely to survive or reproduce.
• Over time, the elimination of individuals that
are not adapted can cause changes to species
of organisms.
Life and Geologic Time
10. • Life scientists often define a species as a group
of organisms that normally reproduces only
with other members of their group.
Species
1
Life and Geologic Time
11. Natural Selection
1
Life and Geologic Time
• Charles Darwin was a naturalist who sailed
around the world from 1831 to 1836 to study
biology and
geology.
12. Natural Selection
1
Life and Geologic Time
• In his book, he proposed that natural
selection is a process by which organisms with
characteristics that are suited to certain
environment have a better chance of surviving
and reproducing than organisms that do not
have these characteristics.
13. • Because many characteristics are inherited, the
characteristics of organisms that are better
adapted to the environment get passed on to
offspring more often.
Natural Selection
1
• According to Darwin, this can cause a species
to change over time.
Life and Geologic Time
14. • A new characteristic
becomes common
in a species only if
some members
already possess that
characteristic and if
the trait increases
the animal’s chance
of survival.
Natural Selection Within a Species
1
Life and Geologic Time
15. • By carefully choosing individuals with
desired characteristics, animal breeders have
created many breeds of cats, dog, cattle, and
chickens.
Artificial Selection
1
• Natural selection explains how
characteristics change and how new species
arise.
Life and Geologic Time
16. • The exoskeleton of a trilobite consists of
three lobes that run the length of the body.
Trilobites
1
• The trilobite’s body also has a head
(cephalon), a segmented middle section
(thorax), and a tail (pygidium).
Life and Geologic Time
17. • Paleontologists can
use these different
characteristics to
demonstrate changes
in trilobites through
geologic time.
Changing Characteristics of
Trilobites
1
Life and Geologic Time
18. Changing Characteristics of
Trilobites
1
• These changes can
tell you about how
different trilobites
from different
periods lived and
responded to
changes in their
environments.
Life and Geologic Time
19. • Trilobite eyes show
the result of natural
selection.
Trilobite Eyes1
Life and Geologic Time
20. Trilobite Eyes
1
Life and Geologic Time
• In most species of trilobites, the eyes were
located midway on the head—a compromise
for an organism that was adapted for crawling
on the seafloor and swimming in the water.
• Over time, the eyes in trilobites changed.
• In many trilobite species, the eyes became
progressively smaller until they completely
disappeared.
21. Trilobite Eyes
1
Life and Geologic Time
• Blind trilobites might have burrowed into
sediments on the seafloor or lived deeper than
light could penetrate.
• In other species,
however, the
eyes became
more complex.
22. Trilobite Eyes
1
Life and Geologic Time
• One kind of trilobite, Aeglina, developed large
compound eyes that had numerous individual
lenses.
• Some trilobites developed stalks that held the
eyes upward.
23. Trilobite Bodies
1
Life and Geologic Time
• The trilobite body and
tail also underwent
significant changes in
form through time.
• It is thought that
Olenellus, and other
species that have so
many body segments,
are primitive trilobites.
24. Fossils Show Changes1
Life and Geologic Time
• Trilobite exoskeletons changed as trilobites
adapted to changing environments.
• Species that could not adapt became extinct.
25. Plate Tectonics and Earth History
• Plate tectonics is
one possible
answer to the
riddle of trilobite
extinction.
• By the end of the Paleozoic Era, sea levels
had dropped and the continents had come
together to form one giant landmass, the
supercontinent Pangaea.
1
Life and Geologic Time
26. Plate Tectonics and Earth History
• Because trilobites lived in the oceans, their
environment was changed or destroyed.
• Not all scientists accept this explanation for
the extinctions at the end of the Paleozoic
Era, and other possibilities—such as climate
change—have been proposed.
1
Life and Geologic Time
27. 1
Question 1
Which of these geologic time subdivisions is
longest?
A. era
B. eon
C. epoch
D. period
Section Check
NC: 5.01
28. 1
Section Check
Answer
The answer is B.
Eons are the longest
subdivisions of
geologic time and
are based upon the
abundance of certain
fossils.
NC: 5.01
29. 1
Question 2
What is organic evolution?
Section Check
Answer
Organic evolution is the change
of species over time.
NC: 5.01, 5.02
30. 1
Question 3
__________ is the process by which organisms
with specific characteristics have a greater
chance of surviving and reproducing than
organisms that do not have those characteristics.
A. Artificial selection
B. Natural selection
C. Organic evolution
D. Predominance
Section Check
NC: 5.02
31. 1
Section Check
Answer
The answer is B. Charles Darwin wrote about
the theory of evolution by natural selection in
his book, The Origin of Species.
NC: 5.02
32. Precambrian Time
• Precambrian time is the longest part of
Earth’s history and includes the Hadean,
Archean, and Proterozoic Eons.
Early Earth History
2
33. Precambrian Time
• Precambrian time lasted from about 4.5
billion years ago to about 544 million years
ago.
Early Earth History
2
34. Precambrian Time
• Although the Precambrian was the longest
interval of geologic time, relatively little is
known about the organisms that lived during
this time.
• One reason is that many Precambrian rocks
have been so deeply buried that they have
been changed by heat and pressure.
Early Earth History
2
35. Precambrian Time
• In addition, most Precambrian organisms
didn’t have hard parts that otherwise would
have increased their chances to be preserved
as fossils.
Early Earth History
2
36. Early Life
• Many studies of the
early history of life
involve ancient
stromatolites.
• Stromatolites are
layered mats formed
by cyanobacteria
colonies.
2
Early Earth History
37. Early Life
• Cyanobactreia are blue-green algae thought
to be one of the earliest forms of life on
Earth. They contained chlorophyll and used
photosynthesis.
• During photosynthesis they produced
oxygen, which helped oxygen become a
major atmospheric gas.
2
Early Earth History
38. Early Life
• Animals without backbones, called
invertebrates, appeared toward the end of
Precambrian time.
• Because these early invertebrates were soft-
bodied, they weren’t often preserved as
fossils. Because of this, many Precambrian
fossils are trace fossils.
2
Early Earth History
39. Unusual Life-Forms
• A group of animals with shapes similar to
modern jellyfish, worms, and soft corals was
living late in Precambrian time.
• This group of organisms has become known
as the Ediacaran fauna.
2
Early Earth History
• Ediacaran animals were bottom dwellers and
might have had tough outer covering like air
mattresses.
40. • The Paleozoic Era, or era of ancient life,
began about 544 million years ago and ended
about 248 million years ago.
The Paleozoic Era
• An abundance of organisms with hard parts,
such as shells, marks the beginning of the
Paleozoic Era.
2
Early Earth History
41. Paleozoic Life
• Many of the life-forms scientists know about
were marine, meaning they lived in the
ocean.
2
Early Earth History
• Trilobites were common, especially early in
the Paleozoic.
• Other organisms developed shells that were
easily preserved as fossils.
• Vertebrates, or animals with backbones, also
evolved during this era.
42. Paleozoic Life
• Armored fish with jaws lived during the
Devonian Period.
2
Early Earth History
• By the Devonian
Period, forests
had appeared and
vertebrates began
to adapt to land
environments, as
well.
43. Life on Land
• Paleontologists know that many ancient fish
had lungs as well as gills.
2
Early Earth History
• Lungs enabled these fish to live in water with
low oxygen levels—when needed they could
swim to the surface and breathe air.
• One kind of ancient fish had lungs and
leglike fins, which were used to swim and
crawl around on the ocean bottom.
44. Life on Land
• Paleontologists hypothesize that amphibians
might have evolved from this kind of fish.
2
Early Earth History
45. • Today amphibians
live in a variety of
habitats in water
and on land.
• They all have at
least one thing in
common, though.
They must lay
their eggs in water
or moist places.
2
Early Earth History
Life on Land
46. • By the Pennsylvanian Period, some
amphibians evolved an egg with a membrane
that protected it from drying out.
• These animals, called reptiles, no longer needed
to lay eggs in water.
2
Early Earth History
Life on Land
• Reptiles also have skin with hard scales that
prevent loss of body fluids.
• This adaptation enables them to survive farther
from water in relatively dry climates.
47. • Several mountain-
building episodes
occurred during the
Paleozoic Era.
2
• The Appalachian
Mountains, for
example, formed
during this time.
Early Earth History
Mountain Building
48. • The first mountain-building episode
occurred as the ocean separating North
America from Europe and Africa closed.
• Several volcanic island chains that had
formed in the ocean collided with the North
American Plate.
2
• The collision of the island chains generated
high mountains.
Mountain Building
Early Earth History
49. • The next mountain-building episode was a
result of the African Plate colliding with the
North American Plate.
• When Africa and North America collided,
rock layers were folded and faulted.
2
• Sediments were uplifted to form an immense
mountain belt, part of which still remains
today.
Mountain Building
Early Earth History
50. • At the end of the
Paleozoic Era, more
than 90 percent of all
marine species, and
70 percent of all land
species died off.
2
End of an Era
Early Earth History
51. • Near the end of the Permian Period, the
continental plates came together and
formed the supercontinent Pangaea.
2
• Mountain-building processes caused seas to
close and deserts to spread over North
America and Europe.
• Many species, especially marine organisms,
couldn’t adapt to these changes, and became
extinct.
End of an Era
Early Earth History
52. • During the late Paleozoic Era, volcanoes were
extremely active. If the volcanic activity was
great enough, it could have affected the entire
globe.
2
• Perhaps a large asteroid or comet collided
with Earth some 248 million years ago.
• Perhaps the extinction was caused by several
or all of these events happening at about the
same time.
Other Hypotheses
Early Earth History
53. 2
Section Check
Question 1
Which was the longest period of
geologic time?
A. Paleozoic Era
B. Pennsylvanian Period
C. Phanerozoic Eon
D. Precambrian Time
NC: 5.01
54. 2
Section Check
Answer
The answer is D.
Precambrian Time was
the longest period of
geologic time, lasting
about 4 billion years.
NC: 5.01
55. 2
Section Check
Question 2
_________ are blue-green algae and are thought
to be one of the earliest forms of life on Earth.
A. Amphibious plants
B. Cyanobacteria
C. Dickensonia
D. Trilobites
NC: 5.01, 5.03
57. 2
Section Check
Question 3
Animals without backbones are called
__________.
A. exvertebrates
B. invertebrates
C. neovertebrates
D. nonvertebrates
NC: 5.01
59. • The Mesozoic Era, or era of middle life,
was a time of many changes on Earth.
3
• At the beginning of the Mesozoic Era, all
continents were joined as a single landmass
called Pangaea.
Middle and Recent Earth History
The Mesozoic Era
The Breakup of Pangaea
60. • Pangaea separated into two large landmasses.
3
• The northern mass was Laurasia, and
Gondwanaland was the southern landmass.
Middle and Recent Earth History
The Mesozoic Era
The Breakup of Pangaea
Click image to view movie.
61. • Reptile’s skin helps it retain bodily fluids.
3
• This characteristic, along with their shelled
eggs, enabled reptiles to adapt readily to the
drier climate of the Mesozoic Era.
Middle and Recent Earth History
The Mesozoic Era
The Breakup of Pangaea
• Reptiles became the most conspicuous
animals on land by the Triassic period.
62. 3
• Dinosaurs ranged in
height from less
that 1 m to
enormous creatures
like Apatosaurus
and Tyrannosaurus.
• Throughout the Mesozoic Era, new species
of dinosaur evolved and other species
became extinct.
Middle and Recent Earth History
Dinosaurs
63. 3
• Some dinosaur tracks indicate that these
animals were much faster runners than you
might think.
• Gallimimus could reach speeds of 65 km/h.
Middle and Recent Earth History
Dinosaurs Were Active
64. 3
• Some studies also indicate that dinosaurs
might have been warm blooded, not cold
blooded like present-day reptiles.
Middle and Recent Earth History
Dinosaurs Were Active
• Slices through some cold-blooded animal
bones show rings similar to growth rings in
trees.
• The bones of some dinosaurs don’t show this
ring structure.
65. 3
• The fossil record also indicates that some
dinosaurs nurtured their young and traveled
in herds in which the adults surrounded their
young.
Middle and Recent Earth History
Good Mother Dinosaurs
66. 3
• One such dinosaur is Maiasaura.
Middle and Recent Earth History
Good Mother Dinosaurs
• This dinosaur built nests in which it laid eggs
and raised its offspring.
• Nests have been found in relatively close
clusters, indicating that more than one family
of dinosaurs built in the same areas.
• Some fossils of hatchlings have been found
near adult animals, leading paleontologists to
think that some dinosaurs nurtured their
young.
67. • Birds appeared during the Jurassic Period.
3
• Some paleontologists think that birds evolved
from small, meat-eating dinosaurs.
• The earliest bird, Archaeopteryx, had wings
and feathers.
Middle and Recent Earth History
Birds
68. • Mammals
first appeared
in the Triassic
Period.
3
• The earliest
mammals
were small,
mouselike
creatures.
Middle and Recent Earth History
Mammals
69. • Mammals are warm-blooded vertebrates
that have hair covering their bodies.
3
• The females produce milk to feed their
young.
Middle and Recent Earth History
Mammals
• These two characteristics have enabled
mammals to survive in many changing
environments.
70. • During most of the Mesozoic Era,
gymnosperms dominated the land.
3
• Gymnosperms are plants that produce seeds
but not flowers.
Middle and Recent Earth History
Gymnosperms
• These include pines and ginkgo trees.
71. • Angiosperms, or flowering plants, first
evolved during the Cretaceous Period.
3
• Angiosperms produce seeds with hard outer
coverings.
Middle and Recent Earth History
Angiosperms
• Because their seeds are enclosed and
protected, angiosperms can live in many
environments.
• Angiosperms are the most diverse and
abundant land plants today.
72. • The Mesozoic Era ended about 65 million
years ago with a major extinction of land and
marine species.
3
Middle and Recent Earth History
End of an Era
• Many paleontologists hypothesize that a
comet or asteroid collided with Earth,
causing a huge cloud of dust and smoke to
rise in the atmosphere, blocking out the Sun.
73. • Without sunlight the plants died, and all
animals that depended on these plants also
died.
3
Middle and Recent Earth History
End of an Era
• All the organisms that you see around you
today are descendants of the survivors of the
great extinction at the end of the Mesozoic
Era.
74. • The Cenozoic Era, or era of recent life,
began about 65 million years ago and
continues today.
3
Middle and Recent Earth History
The Cenozoic Era
• The Cenozoic Era is subdivided into two
periods.
• The first of these is the Tertiary period.
• The present-day period is the Quaternary
Period. It began about 1.8 million years ago.
75. • Many mountain ranges
formed during the
Cenozoic Era.
3
Middle and Recent Earth History
Times of Mountain Building
• These include the
Alps in Europe and
the Andes in South
America.
76. • The Himalaya
formed as
India moved
northward and
collided with
Asia.
3
Middle and Recent Earth History
Times of Mountain Building
• The collision crumpled and thickened Earth’s
crust, raising the highest mountains presently
on Earth.
77. • Throughout much of the Cenozoic Era,
expanding grasslands favored grazing plant
eaters like horses, camels, deer, and some
elephants.
3
Middle and Recent Earth History
Further Evolution of Mammals
• Many kinds of
mammals became
larger.
78. • Not all mammals remained on land.
3
Middle and Recent Earth History
Further Evolution of Mammals
• Ancestors of the present-day whales and
dolphins evolved to live in the sea.
79. • As Australia and South America separated
from Antarctica during the continuing
breakup of the continents, many species
became isolated.
3
Middle and Recent Earth History
Further Evolution of Mammals
• They evolved separately from life-forms in
other parts of the world.
80. • Evidence of this can be seen today in
Australia’s marsupials.
3
Middle and Recent Earth History
Further Evolution of Mammals
• Marsupials are mammals such as kangaroos,
koalas, and wombats that carry their young in
a pouch.
81. • Your species, Homo sapiens, probably
appeared about 140,000 years ago.
3
Middle and Recent Earth History
Further Evolution of Mammals
• Some people suggest that the appearance of
humans could have led to the extinction of
other mammals.
• As their numbers grew, humans competed for
food that other animals relied upon.
82. 3
Section Check
Question 1
During which time
period did Pangaea
separate?
A. Devonian
B. Mississippian
C. Permian
D. Triassic
NC: 5.01,
5.02, 5.03
83. 3
Section Check
Answer
The answer is D. Pangaea separated into two
large landmasses, Laurasia and Gondwanaland,
during the Triassic Period.
NC: 5.01,
5.02, 5.03
84. 3
Section Check
Question 2
The era of recent life is the __________.
A. Cenozoic Era
B. Mesozoic Era
C. Paleozoic Era
D. Precambrian Time
NC: 5.01
86. 3
Section Check
Question 3
What were the dominant land animals of the
Mesozoic Era?
A. Dinosaurs
B. Gymnosperms
C. Predatory fish
D. Trilobites
NC: 5.01, 5.03
87. 3
Section Check
Answer
The answer is A. Dinosaurs were the
dominant land animals of the Mesozoic Era.
Gymnosperms were the dominant plants.
NC: 5.01, 5.03
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